This invention relates to a composite bearing in which to a backing metal is bonded a resin layer in which polytetrafluoroethylene (referred to hereinafter as PTFE) is added to a base resin consisting essentially of polyether ether ketone (referred to hereinafter as PEEK).
As composite bearings to be incorporated into a generator, a pump or the like, bearings in which a resin layer is bonded to a backing metal have heretofore been known.
In recent years, with a tendency of a bearing device to be miniaturized, the bearing in the device has been miniaturized and a higher surface pressure has come to be applied. A composite bearing applied under such severe conditions is required to have not only excellent sliding characteristics but also various properties such as high mechanical strength and the like.
A bearing which is repeatedly subjected to, for example, starting and stopping requires a great starting power because at the time of starting, the sliding surface of the bearing is partially in solid contact with a shaft or a pin, and there is a fear that this may result in peeling of the resin layer per se and in peeling and damaging of the bonding portion between the backing metal and the resin layer. Therefore, the bearing has been required to have, in addition to wear resistance and the like during the operation, a small coefficient of friction at the time of starting and required to be excellent in peeling strength of the resin layer per se and bonding force between the backing metal and the resin layer.
As the sliding material for the bearing, there have been known resin materials in which PEEK is used as a base resin and has added thereto PTFE and carbon fiber, and the like.
PEEK is an engineering resin having excellent heat resistance, mechanical properties and wear resistance; however, when PEEK is used alone, the coefficient of friction is high, so that a resin having a low coefficient of friction such as PTFE or the like is added to the PEEK to lower the coefficient of friction thereof. On the other side, however, it is known that the addition of PTFE results in deterioration of mechanical strength. The technique disclosed in JP-A 58(1983)-160,346 teaches, as a sliding material to be used under the dry conditions, a resin consisting essentially of PEEK as the base material and also contains 2.5 to 60% by weight of PTFE and 2.5 to 60% by weight of carbon fibers. In the above publication, it is stated that a high heat distortion temperature (HDT) and a high limiting PV value are obtained with this resin composition.
Moreover, in JP-A 9(1997)-157,532 of the present inventors, as a sliding material for bearing, there is proposed a sliding resin composed of PEEK having added hereto 0.1 to 8.5% by weight of PTFE and 10 to 45% by weight of carbon fibers, based on the sliding resin. It is stated that with this composition, a sliding material excellent in wear resistance is obtained.
These inventions aim at adding carbon fiber to a base resin to improve the mechanical strength and wear resistance, and adding PTFE to the base resin to lower the coefficient of friction.